Q: For the reaction $2NO_2(g) \rightarrow 2NO(g) + O_2(g)$, which expression correctly relates the rate of disappearance of $NO_2$ to the rate of appearance of $O_2$?

$\text{Rate} = -\frac{d[NO_2]}{dt} = 2 \frac{d[NO]}{dt} = \frac{d[O_2]}{dt}$

Question 1

Which of the following best describes the effect on the rate constant $k$ when the temperature of a reaction is increased, according to the Arrhenius equation?

Accepted Answer

The rate constant $k$ increases exponentially with increasing temperature.

Question 2

A reaction is found to be first order with respect to reactant A. Which integrated rate law should be used to determine the concentration of A at time $t$?

Accepted Answer

$[A]_t = [A]_0 e^{-kt}$

Question 3

For the reaction $2NO_2(g) \rightarrow 2NO(g) + O_2(g)$, which expression correctly relates the rate of disappearance of $NO_2$ to the rate of appearance of $O_2$?

Accepted Answer

$	ext{Rate} = -\frac{d[NO_2]}{dt} = 2 \frac{d[NO]}{dt} = \frac{d[O_2]}{dt}$

Question 4

If the rate law for a reaction is $	ext{Rate} = k[A][B]^2$, what is the overall order of the reaction?

Accepted Answer

Third order

Question 5

Which statement best describes Le Châtelier's Principle?

Accepted Answer

A system at equilibrium will shift to counteract any imposed change in concentration, pressure, or temperature.

Question 6

For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, the equilibrium constant $K_c$ is given by:

Accepted Answer

$K_c = \frac{[NH_3]^2}{[N_2][H_2]^3}$

Question 7

A reaction mechanism consists of the following steps:
Step 1: $A + B \rightarrow C$ (slow)
Step 2: $C \rightarrow D$ (fast)
Which step determines the overall rate law?

Accepted Answer

Step 1, because the slowest step in a mechanism is the rate-determining step.

Question 8

Which of the following changes will increase the yield of ammonia in the Haber process ($N_2 + 3H_2 \rightleftharpoons 2NH_3$) at equilibrium?

Accepted Answer

Increasing the pressure

Question 9

Given the equilibrium $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, if the concentration of $SO_2$ is doubled, what happens to the equilibrium position?

Accepted Answer

The equilibrium shifts to the right, favoring products.

Question 10

Which of the following correctly relates $K_p$ and $K_c$ for the reaction $aA(g) + bB(g) \rightleftharpoons cC(g) + dD(g)$?

Accepted Answer

$K_p = K_c (RT)^{\Delta n}$, where $\Delta n = (c + d) - (a + b)$

Question 11

A second-order reaction has a half-life given by which of the following equations?

Accepted Answer

$t_{1/2} = \frac{1}{k[A]_0}$

Question 12

Which of the following is true about the equilibrium constant $K$ for a reaction?

Accepted Answer

It changes only with temperature.

Question 13

For the reaction $A \rightarrow B$, the initial concentration of $A$ is $0.50$ M. After $10$ minutes, the concentration of $A$ is $0.25$ M. If the reaction is first order, what is the rate constant $k$?

Accepted Answer

$k = \frac{1}{10} \ln(0.5/0.25)$

Question 14

Which of the following is NOT a valid assumption for the steady-state approximation in reaction mechanisms?

Accepted Answer

The intermediate is present in high concentration throughout the reaction.

Question 15

A catalyst increases the rate of a chemical reaction by:

Accepted Answer

Lowering the activation energy $E_a$

Question 16

If the equilibrium constant $K$ for a reaction is much less than 1, which statement is true?

Accepted Answer

The reaction strongly favors reactants at equilibrium.

Question 17

For the reaction $A + B \rightarrow C$, doubling the concentration of $A$ doubles the rate, but doubling $B$ quadruples the rate. What is the rate law?

Accepted Answer

$	ext{Rate} = k[A][B]^2$

Question 18

Which of the following is true about the relationship between $Q$ and $K$ for a chemical reaction?

Accepted Answer

If $Q < K$, the reaction will shift toward products to reach equilibrium.

Question 19

A student is studying the decomposition of hydrogen peroxide: $2H_2O_2 \rightarrow 2H_2O + O_2$. If the rate of disappearance of $H_2O_2$ is $0.10$ M/s, what is the rate of appearance of $O_2$?

Accepted Answer

$0.05$ M/s

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